main: Let the X11 CM backend deal with selecting the display

It's specific to that backend, so do it there.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1833>

src/backends/x11/cm/meta-backend-x11-cm.c

@@ -37,10 +37,23 @@
 #include "compositor/meta-compositor-x11.h"
 #include "core/display-private.h"
 
+enum
+{
+  PROP_0,
+
+  PROP_DISPLAY_NAME,
+
+  N_PROPS
+};
+
+static GParamSpec *obj_props[N_PROPS];
+
 struct _MetaBackendX11Cm
 {
   MetaBackendX11 parent;
 
+  char *display_name;
+
   MetaCursorRenderer *cursor_renderer;
   char *keymap_layouts;
   char *keymap_variants;
@@ -437,6 +450,50 @@ meta_backend_x11_cm_translate_crossing_event (MetaBackendX11 *x11,
     }
 }
 
+static void
+meta_backend_x11_cm_set_property (GObject      *object,
+                                  guint         prop_id,
+                                  const GValue *value,
+                                  GParamSpec   *pspec)
+{
+  MetaBackendX11Cm *backend_x11_cm = META_BACKEND_X11_CM (object);
+
+  switch (prop_id)
+    {
+    case PROP_DISPLAY_NAME:
+      backend_x11_cm->display_name = g_value_dup_string (value);
+      break;
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+    }
+}
+
+static void
+meta_backend_x11_cm_finalize (GObject *object)
+{
+  MetaBackendX11Cm *x11_cm = META_BACKEND_X11_CM (object);
+
+  g_clear_pointer (&x11_cm->display_name, g_free);
+}
+
+static void
+meta_backend_x11_cm_constructed (GObject *object)
+{
+  MetaBackendX11Cm *x11_cm = META_BACKEND_X11_CM (object);
+  const char *display_name;
+
+  if (x11_cm->display_name)
+    display_name = (const char *) x11_cm->display_name;
+  else
+    display_name = g_getenv ("MUTTER_DISPLAY");
+
+  if (display_name)
+    g_setenv ("DISPLAY", display_name, TRUE);
+
+  G_OBJECT_CLASS (meta_backend_x11_cm_parent_class)->constructed (object);
+}
+
 static void
 meta_backend_x11_cm_init (MetaBackendX11Cm *backend_x11_cm)
 {
@@ -455,9 +512,14 @@ meta_backend_x11_cm_init (MetaBackendX11Cm *backend_x11_cm)
 static void
 meta_backend_x11_cm_class_init (MetaBackendX11CmClass *klass)
 {
+  GObjectClass *object_class = G_OBJECT_CLASS (klass);
   MetaBackendClass *backend_class = META_BACKEND_CLASS (klass);
   MetaBackendX11Class *backend_x11_class = META_BACKEND_X11_CLASS (klass);
 
+  object_class->set_property = meta_backend_x11_cm_set_property;
+  object_class->finalize = meta_backend_x11_cm_finalize;
+  object_class->constructed = meta_backend_x11_cm_constructed;
+
   backend_class->post_init = meta_backend_x11_cm_post_init;
   backend_class->create_renderer = meta_backend_x11_cm_create_renderer;
   backend_class->create_monitor_manager = meta_backend_x11_cm_create_monitor_manager;
@@ -472,5 +534,15 @@ meta_backend_x11_cm_class_init (MetaBackendX11CmClass *klass)
   backend_x11_class->handle_host_xevent = meta_backend_x11_cm_handle_host_xevent;
   backend_x11_class->translate_device_event = meta_backend_x11_cm_translate_device_event;
   backend_x11_class->translate_crossing_event = meta_backend_x11_cm_translate_crossing_event;
+
+  obj_props[PROP_DISPLAY_NAME] =
+    g_param_spec_string ("display-name",
+                         "display name",
+                         "X11 display name",
+                         NULL,
+                         G_PARAM_WRITABLE |
+                         G_PARAM_CONSTRUCT_ONLY |
+                         G_PARAM_STATIC_STRINGS);
+  g_object_class_install_properties (object_class, N_PROPS, obj_props);
 }
 

src/core/main.c

@@ -303,28 +303,6 @@ meta_get_option_context (void)
   return ctx;
 }
 
-/**
- * meta_select_display:
- *
- * Selects which display Mutter should use. It first tries to use
- * @display_name as the display. If @display_name is %NULL then
- * try to use the environment variable MUTTER_DISPLAY. If that
- * also is %NULL, use the default - :0.0
- */
-static void
-meta_select_display (char *display_arg)
-{
-  const char *display_name;
-
-  if (display_arg)
-    display_name = (const char *) display_arg;
-  else
-    display_name = g_getenv ("MUTTER_DISPLAY");
-
-  if (display_name)
-    g_setenv ("DISPLAY", display_name, TRUE);
-}
-
 void
 meta_finalize (void)
 {
@@ -653,6 +631,19 @@ calculate_compositor_configuration (MetaCompositorType  *compositor_type,
   else
 #endif /* HAVE_WAYLAND */
     {
+      static const char *display_name_prop_names[] = {
+        "display-name",
+      };
+      static GValue display_name_prop_values[] = {
+        G_VALUE_INIT,
+      };
+
+      g_value_init (&display_name_prop_values[0], G_TYPE_STRING);
+      g_value_set_string (&display_name_prop_values[0], opt_display_name);
+
+      *n_properties = G_N_ELEMENTS (display_name_prop_values);
+      *prop_names = display_name_prop_names;
+      *prop_values = display_name_prop_values;
       *backend_gtype = META_TYPE_BACKEND_X11_CM;
       return;
     }
@@ -793,11 +784,6 @@ meta_init (void)
   g_irepository_prepend_search_path (MUTTER_PKGLIBDIR);
 #endif
 
-  /* NB: When running as a hybrid wayland compositor we run our own headless X
-   * server so the user can't control the X display to connect too. */
-  if (!meta_is_wayland_compositor ())
-    meta_select_display (opt_display_name);
-
   meta_init_backend (backend_gtype, n_properties, prop_names, prop_values);
 
   for (i = 0; i < n_properties; i++)